exec()

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Published Aug 24, 2023
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The exec() function executes a code object or string containing Python code.

Syntax

exec(object, globals=None, locals=None)
  • object : String or code object
  • globals: (optional) A dictionary containing global variables. If not specified, defaults to None.
  • locals: (optional) A dictionary containing local variables. If not specified, defaults to None.

The exec() function returns None.

Example 1

This example uses exec() to parse and execute Python code contained in the string code:

code = 'print("Hello, Codecademy!")'
exec(code)

This example results in the following output:

Hello, Codecademy!

Example 2

This example uses exec() to execute Python code from a file code.txt, which contains Python commands:

#code.txt
import datetime
current_time = datetime.datetime.now()
print(current_time)

The content of the file code.txt is read until the end of the file (EOF) into a string. The content (Python commands) is executed by exec().

with open('code.txt','r') as file:
code = file.read()
exec(code)

This example will produce output like the following, but with the current date:

2023-08-16 14:17:06.092145

Example 3

This example uses exec() with globals and locals:

code = input("Enter your command: ")
# In this example a user could inject malicious code like "import os; os.system('cat /etc/passwd')"
exec(code)
code = input("Enter another command: ")
# The globals dictionary allows only the print function from the builtins.
exec(code,{"__builtins__": {"print": print}},{})
def f1():
print('Hello, Codecademy!')
def f2():
print('Hello, world!')
# locals restrict the usage of f1 function with exec:
exec("f1()",{"__builtins__": {}}, {"f1": f1})
exec("f2()",{"__builtins__": {}}, {"f1": f1}) # This will throw an error

Codebyte Example

This example uses exec() to execute a code object:

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